What to do in a thunderstorm comes down to one rule: get inside a substantial building or a hard-topped metal vehicle as soon as you hear thunder, and stay there until 30 minutes after the last rumble. If you can hear thunder, you are close enough to be struck, even if it is not raining yet and the sky overhead looks clear.
Many lightning injuries happen at the start and end of a storm, when people think it has not arrived yet or has already passed. Here is how to judge the distance and where to shelter at home, outdoors, in a car or a tent.
Key takeaways
- "When thunder roars, go indoors" is the core lightning safety rule of the US National Weather Service (NWS).
- Thunder takes about 5 seconds to travel 1 mile (3 seconds per kilometer), so counting from flash to bang tells you how far away the lightning is.
- Lightning can strike as far as 10 miles (16 km) from the rain, so no place outside is safe while a storm is nearby.
- A house with wiring and plumbing or a hard-topped metal car is safe; a tree, tent, shed, porch or picnic shelter is not.
- A person struck by lightning carries no charge: call 911 (US and Canada), 999 (UK), 112 (EU) or 000 (Australia) and start CPR if they are not breathing.
How does lightning form?
Lightning forms inside cumulonimbus clouds, when strong updrafts make ice crystals, supercooled droplets and soft hail collide. The collisions transfer electric charge: lighter particles carry positive charge to the top of the cloud, while heavier ones keep negative charge lower down.
When the difference in charge between the cloud and the ground, or between two parts of the cloud, overcomes the resistance of the air, a discharge occurs. According to the NWS, the air in the lightning channel can reach about 50,000 °F (27,700 °C), five times hotter than the surface of the sun. The air expands explosively, and that shock wave is thunder. The same updrafts that separate the charges also build hail inside the cloud, which is why severe storms often bring both.
How can you tell how far away lightning is?
To tell how far away lightning is, count the seconds between the flash and the thunder, then divide by 5 for miles or by 3 for kilometers. Light arrives almost instantly, while sound travels about a mile every 5 seconds.
| Seconds from flash to thunder | Approximate distance | What it means |
|---|---|---|
| 60 seconds | 12 miles (20 km) | The storm is within hearing range: head indoors |
| 30 seconds | 6 miles (10 km) | Within striking distance: you should already be inside |
| 15 seconds | 3 miles (5 km) | Immediate danger |
| 5 seconds | 1 mile (1.7 km) | Lightning is very close |
| Flash and bang together | Overhead | Stay inside, away from windows and plumbing |
If you cannot hear thunder because of wind, traffic or a loud event, do not assume you are safe. "Bolts from the blue" can strike up to 10 miles (16 km) from the parent storm, outside the area where rain is falling.
What is the 30-30 rule for lightning?
The 30-30 rule is a lightning safety guideline with two parts: if 30 seconds or less pass between the flash and the thunder, get to shelter, and once inside, wait 30 minutes after the last thunder before going back out. The first part tells you when to go in; the second tells you when it is safe to leave.
The NWS puts it even more simply: when thunder roars, go indoors. Any audible thunder means you are within reach of lightning, so there is no need to wait for the count to drop to 30 seconds.
The second half is the one people forget: as the rain eases, the back of the storm can still produce lightning, just as a game or a beach day resumes.
Where is it safe to be during a thunderstorm?
The safest place in a thunderstorm is a fully enclosed building with wiring and plumbing, because a strike follows the wires and pipes to the ground. The second best is a hard-topped metal vehicle with the windows closed.
| Place | Safe? | Why |
|---|---|---|
| House, office, shopping mall | Yes | The structure carries the current to the ground |
| Hard-topped car, bus or van | Yes | The metal body carries the current around you |
| Convertible or soft-top car | No | No metal shell surrounds the occupants |
| Under a tree | No | Lightning strikes the high point and can jump to you |
| Tent, shed, porch, picnic shelter, dugout | No | They offer no lightning protection |
| Beach, pool, lake or small boat | No | Water and lack of shelter raise the risk |
| Summit, ridge or open field | No | You are the highest point around |
What to do in a thunderstorm in a car
In a car, the protection comes from the metal around you, not from the rubber tires. Keep the windows up, avoid touching metal parts inside and, if visibility drops, pull over somewhere safe with your hazard lights on until the worst passes.
What to do in a thunderstorm outside
If you are caught outside in a thunderstorm with no building or car nearby, there is no safe place, but some spots are far worse than others. Move toward lower ground and keep going toward shelter rather than waiting in the open.
- Get off high ground: hills, ridges and peaks receive the most strikes.
- Get out of the water: leave the pool, sea, lake or river and move away from the shore.
- Avoid isolated trees and tall objects: fences, power lines, metal poles and the cables of climbing routes can carry current a long way.
- Spread out: in a group, keep several meters apart so one strike cannot hit everyone.
- Never lie flat on the ground.
Some outdoor guides describe crouching low with your feet together as a last resort if your hair stands on end. It does not make you safe, so never use it instead of moving to shelter.
What to do in a thunderstorm when camping or hiking
When camping, backpacking or hiking in the mountains, the best protection is timing. In many mountain ranges, summer storms build from late morning or early afternoon, so start early and plan to be off summits and exposed ridges by midday. A tent offers no protection: if a storm hits, head for a car or a solid building if you can reach one, or for lower, more sheltered ground.
What to do in a thunderstorm in a house
In a house during a thunderstorm, the main precaution is to avoid contact with anything that can carry current in from outside: wiring, pipes and running water. A strike on or near the building can travel through those systems.
- Do not shower, bathe or wash dishes while the storm is overhead.
- Avoid corded phones and devices plugged into the mains; mobile phones and battery devices are fine.
- Unplug computers, TVs and routers if they have no surge protection.
- Stay away from windows, outside doors, balconies and porches.
- If the storm brings heavy rain or hail, check that outdoor drains are clear.
Which lightning myths are false?
Several lightning myths are false and can lead to dangerous decisions. These are the most common:
- "Lightning never strikes the same place twice." False: tall structures are hit again and again. NOAA estimates the Empire State Building in New York is struck about 23 times a year.
- "Rubber tires protect you in a car." False: the metal body protects you, not a few centimeters of rubber.
- "If it is not raining, there is no danger." False: lightning can strike miles from the rain.
- "Mobile phones attract lightning." There is no evidence for this; being outdoors is what puts you at risk.
- "Touching a lightning victim will shock you." False: the body does not hold a charge. Call the emergency number and start CPR if the person is not breathing.
US lightning deaths have fallen sharply since the mid-20th century, but the NWS still counted 20 in 2025.
How to anticipate a thunderstorm with Clima de Hoy
Clima de Hoy helps you see in advance when thundery showers are most likely in your area. Check the hourly forecast for Miami, where summer afternoon storms are common, or the hourly forecast for Madrid before a trip: when storms appear, note the hours where the chance of rain and the forecast amounts peak.
The rain forecast map shows where the models expect showers to move over the coming hours. To follow a real storm minute by minute, use a live radar from your national weather service; our guide on how to read weather radar explains how. If a warning is issued, see what each weather warning color means.
Frequently asked questions
Is it safe to be in a car during a thunderstorm?
Yes, as long as the car has a hard metal roof and body and the windows are closed. If lightning strikes, the current flows through the metal shell to the ground without passing through the cabin. Convertibles, motorcycles and bicycles offer no protection.
How long should you wait after a thunderstorm to go outside?
Wait 30 minutes after the last thunder you hear. Even if the rain has stopped and the sun is out, the trailing part of the storm can still send lightning several miles ahead of or behind it.
Can you use your phone during a thunderstorm?
Yes, mobile phones and any battery-powered device without a cable are safe to use indoors. What you should avoid are corded landline phones and devices plugged into the mains, because a strike can travel through the wiring.
What should you do if someone is struck by lightning?
Call the emergency number right away: 911 in the US and Canada, 999 in the UK, 112 in the EU or 000 in Australia. The person carries no electric charge, so it is safe to touch them. If they are not breathing, start CPR and use a defibrillator if one is available.
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